The present invention relates to an electrostatic recording apparatus, and in particular, to a method of controlling a surface potential of a photoconductive member or body and a method of evaluating a life thereof by detecting a surface state of the photoconductive member by use of surface potential detect means and to an electrostatic recording apparatus suitable for the methods above.
In the electrostatic recording apparatus, in general, a photoconductive member of body is charged with electricity so as to effect an exposure of an optical image to produce an electrostatic latent image, which is then developed to obtain a toner image on the photoconductive member. Thereafter, the toner image is transcribed onto a sheet of paper so as to fix the image on the sheet, thereby achieving a recording operation. In this process, the amount of electricity charged on the photoconductive member, namely, the level of an electric potential of the member determines the effect of the electrostatic recording process, and hence there is disposed a control mechanism associated therewith.
There has been filed a patent application (JP-61-56514corresponding to JP-A-54-37760) in which a portion of a photoconductive sheet is rolled on a photoconductive drum such that a utilization portion of the sheet is changed by winding up the sheet and in which for the photoconductive sheet of the winding type, a cap portion of an opening disposed on the drum to pass the photoconductive sheet in the forward and backward directions is set to a ground potential in any situation or the cap potential is set to the ground potential when the cap portion is located at a position opposing to surface potential detect means. An object of this system is that a zero potential correction is conducted on the surface potential detect means when the surface potential detect means passes the cap portion. Another object thereof is to measure the surface potential of the photoconductive member by use of the surface potential detect means so as to control a charging device or charger.
In either case, the potential of the cap portion is open or is set to the ground potential.
On the other hand, the JP-A-58-4172 describes a system in which when the cap portion is set to a location opposing to the surface potential detect means, a calibration voltage is connected to the cap portion so as to calibrate the surface potential detect means, or the cap portion is connected to an ammeter to measure a corona current so as to adjust an output from the power source of the charging device.
According to the technology described above, the cap portion (reference potential measure section) disposed in a portion of the surface of the photoconductive member or body is employed as an electrode to calibrate the surface potential detect means or as an electrode to detect the corona current of the charging device.